1. Field the Invention
The present invention relates to a combustion chamber having fuel/air premixing.
2. Discussion of Background
In modern combustion chambers of gas turbines, premix burners which can be operated on a lean mixture are used in order to limit to a minimum the pollutant components, in particular NOx and CO, arising from the combustion. In principle, it is nowadays assumed that very low NOx emission values, below 10 vppm at 15% O2, must be ensured even at very high flame temperatures. In order to be able to achieve such low pollutant emissions during the operation of a gas turbine over a load range of about 40-100%, a perfectly premixed burner has to be ensured over a wide flame-temperature range, typically about 1650.degree.-1850.degree. K. Such burners are characterized in that a conventional air/fuel premix section is followed by a combustion chamber whose cross section of flow is several times larger than the outlet cross section of the mixing section as a result of an essentially immediate jump in cross section. As a result of this configuration, outer recirculation zones form in the combustion chamber in the region of the plane of this transition, which recirculation zones in fact induce stabilization of the premix flame. However, the stabilizing effect of these recirculation zones relative to the premix flame, i.e. relative to the backflow zone forming in the plane of the outlet cross section of the mixing section, depends substantially on how far the hot gases from the combustion can flow back into these recirculation zones in the course of operation and can maintain the feeding there to form a self-igniting combustion zone or at least a combustion zone burning in a stable manner. Especially in the transient ranges, starting, stopping, changing the operating parameters, etc., the backflow of the hot gases into the recirculation zones may take place irregularly, so that their effect on the outflowing mixture is repressed. In such a configuration, the stabilizing effect of the recirculation zones on the outflowing mixture is lost, whereupon extremely detrimental flame extinction and deflagrations may occur.